1. Field of Invention
This invention relates to the field of defect detection in dielectric materials, and more particularly to a method and apparatus for discovering small defects in the silicon dioxide layers of integrated circuit devices. The invention is especially adapted to discovering defects with a diameter between 10 and 100,000 angstroms in a silicon dioxide ("oxide") layer of an integrated circuit, however, the invention is equally useful for detecting defects in any dielectric which can be located on a conductor.
2. Description of the Prior Art
Prior art detection techniques were limited to detecting only surface passivation defects. These techniques, generally referred to as reverse carbon decoration, deposit a thick carbon layer on the surface of the dielectric.
Reverse carbon deposition was a two step process. The first step of the process exposed the dielectric to a stationary electric field. A large charge was deposited on the surface of the dielectric to a potential of several hundred volts/cm.sup.2. The second step of the process was to deposit an indicator on the surface of the dielectric. The carbon particles were attracted to the charge and left a thick layer of carbon on the surface of the dielectric. The dielectric was then examined for defects which were located where the carbon was not.
The prior art techniques has many problems. One serious problem is that the carbon layer obscured the veiw of the wafer making it difficult to locate the defects relative to the other circuitry located on the wafer. This severely complicates solving the problem. Prior art techniques also could not detect defects in varying oxide thicknesses since these variations could be mistaken as defects.
What is needed is a method and apparatus for detecting small and large defects in a dielectric which varies in thickness.